Historically, highly branched alkylbenzenesulfonate surfactants, such as those based on tetrapropylene (known as “ABS”) were used in detergents. However, these highly branched materials were found to exhibit very poor biodegradability. As a result, subsequent efforts at improving manufacturing processes for alkylbenzenesulfonates were mainly directed at making the alkyl moities as linear as practically possible. Thus the overwhelming proportion of a large volume of prior art relating to alkylbenzenesulfonate surfactant manufacture is directed to the objective of achieving linearity. Moreover all large-scale commercial alkylbenzenesulfonate processes in use today are directed to the production of linear alkylbenzenesulfonates (“LAS”). Typically, these processes involve initially alkylating benzene with a linear olefin in the presence of a homogeneous acid catalyst, such as AlCl3 or HF, and then sulfonating the alkylated benzene.
However, current linear alkylbenzenesulfonates have significant limitations in that, for example, they have limited hard water and/or cold water cleaning properties. Thus, LAS surfactants often fail to produce good cleaning results, for example when formulated with non-phosphate builders and/or when used in hard water areas.
As a result of the limitations of LAS surfactants, consumer cleaning formulations frequently include higher levels of cosurfactants, builders, and other additives than would be needed with a superior alkylbenzenesulfonate. Accordingly, it would be desirable to simplify detergent formulations and deliver both better performance and better value to the consumer. Moreover, in view of the very large volumes of alkylbenzenesulfonate surfactants and detergent formulations used worldwide, even modest improvements in performance of the basic alkylbenzenesulfonate detergent would be of great significance in the marketplace.
In contrast with the conventional understanding as to the importance of linearity in alkylbenzenesulfonates, U.S. Pat. No. 5,026,933 teaches that lightly branched olefin oligomers produced by the oligomerization of lower olefins over surface-deactivated ZSM-23 can be used to alkylate benzene to produce long chain alkylbenzenes which, when sulfonated, yield surfactants which exhibit similar biodegradability properties to equivalent LAS materials. The '933 patent teaches that the alkylation catalyst required to achieve these advantageous results is a heterogeneous crystalline zeolite catalyst having a pore size of 6 to 7 Angstrom, such as dealuminated mordenite.
More recent work reported in, for example, U.S. Pat. No. 6,274,540, has confirmed the findings in the '933 patent and demonstrated that alkylaryl sulfonate surfactants having good biodegradability and cold water solubility can be produced from alkylaromatic hydrocarbon mixtures in which the alkyl moieties have a main chain with 5 to 20 carbons atoms and one or more crystallinity-disrupting groups. The alkylaryl sulfonate surfactants have a Krafft Temperature of no more than 40° C., preferably no more than 5° C., a percentage biodegradation exceeding that of tetrapropylene benzene sulfonate, a weight ratio of nonquaternary to quaternary carbon atoms in the alkyl moiety of at least 5, preferably at least 100, and contain at least 60 wt %, and preferably at least 80 wt %, of isomers in which the aryl group is attached to the second or third carbon atom of the primary alkyl chain.
Similar results are reported in U.S. Pat. No. 6,306,817 in which the alkylaryl sulfonate is composed of at least 2 isomers each having an acyclic aliphatic chain with 6 to 20 carbon atoms and at least one C1-C3 side chain, a weight ratio of nonquaternary to quaternary carbon atoms in the alkyl moiety of at least 10, preferably at least 100, a weight loss of no more than 40 wt %, preferably no more than 10 wt %, in a Hardness Tolerance test, and containing at least 60% of isomers in which the aryl group is attached to the second and third carbon atoms of the primary alkyl chain. According to the '817 patent, the preferred alkylaryl sulfonate consists entirely of isomers in which the aryl group is attached to the second and third carbon atoms of the primary alkyl chain, but no directions are provided as to how to achieve this result.
Typically the surfactants disclosed in the '540 and '817 patents are produced by alkylating an aromatic compound, such as benzene or toluene, with a skeletally isomerized linear olefin in the presence of a mordenite catalyst.
In accordance with the present invention, it has now been found that by using different catalysts from those disclosed in the '933, '540 and '817 patents, it is possible to alkylate an aromatic compound with lightly branched olefin oligomers to produce alkylaromatic compositions which, when sulfonated, produce alkylarylsulfonate surfactants having improved properties, such as biodegradability and hard and cold water performance, as compared with conventional LAS products.